1. Field of the Invention
This invention relates to flexible hoses, and more particularly, to flexible hoses used for conveying fluids in heating and cooling systems.
2. Discussion
Conventional multi-layer hoses used in heating and cooling systems typically include inner and outer elastomeric layers and an intermediate reinforcing layer. The inner layer or core tube defines a flexible flow path for transporting fluids (liquids or gases) from one point to another in the heating and cooling system, and the outer layer protects the hose from cuts, abrasions and other environmental hazards. The elastomeric layers are usually made of polymers such as styrene butadiene copolymer rubber, polychloroprene and ethylene-propylene-diene monomer rubber (EPDM rubber), which provide good flexibility, toughness, and fluid impermeability. The reinforcing layer, which prevents excessive expansion of the inner layer when the core fluid is under pressure, can be fabricated from knitted, braided, or spiral wound synthetic yarn, including nylon, rayon, or glass fibers.
One difficulty with conventional hoses used in heating and cooling systems is inadequate heat resistance. Although multi-layer hoses perform well at ambient temperatures, many fail prematurely when exposed to high temperaturesxe2x80x94as found, for example, in the engine compartments of motor vehicles. Such failures often occur because prolonged exposure to high temperatures (e.g., about 165xc2x0 C. or greater) affects the structure of the polymers that make up the elastomeric layers. The resulting heat-aged hose is less resilient and is prone to crack when flexed.
The present invention provides a flexible multi-layer hose exhibiting improved heat resistance when tested in accordance with ASTM D573-01. The hose includes an elastomeric inner layer or core tube, an intermediate reinforcing layer disposed around the inner layer, and an elastomeric outer layer or protective cover disposed around the reinforcing layer. The intermediate layer comprises a woven fiber, and the inner and outer layers each includes a cross-linked polymer blend. The polymer blend includes a substantial fraction of ethylene-octene copolymer, and optionally, one or more compatible polymers such as chlorosulfonated polyethylene, chlorinated polyethylene, and EPDM. The ethylene-octene copolymer comprises from about forty to about one hundred parts by weight of the polymer blend, and the compatible polymers comprise from about zero to about sixty parts by weight of the polymer blend. The inner and outer layers may have the same or different formulation, and may also contain one or more solid fillers and liquid extenders (i.e., plasticizers). Useful solid fillers include carbon black and calcium carbonate; useful plasticizers include paraffinic oils. The polymer blend is usually cross-linked using a curing agent and an activator, such as an organic peroxide and zinc oxide, respectively. The inner and outer layers may include various additives such as antioxidants.